As the impaired directional flow of cerebrospinal fluid underlies motile cilia dysfunction-induced congenital hydrocephalus (Lee, 2013), we reason that the directional flow of cerebrospinal fluid is maintained in Cep131-deficient mice by the majority of normally beating cilia (Figure 5E and F) until the paralyzed cilia increase to a percentage that seriously disturbs the flow in aged mice. The gene discussed is CEP131; the disease is congenital hydrocephalus.